In the text below reference is made to the following prior art documents:    (1) Carter, A. D. Weed Res., 2000, 40, 113-122.    (2) Motzer, W. E. Environmental Forensics 2001, 2, 301-311.    (3) Urbansky, E. T. Environ. Sci. & Pollut. Res., 2002, 9, 187-192.    (4) Lagaly, G. In: Proc. of the 10th International Clay ConferencSurface and interlayer reactions. Churchman, G. J., Fitzpatrick, R. W. & Egglegton, R. A. Eds.; CSIRO Pub.: Melbourne, Australia, 1995; pp. 137-144.    (5) Xu, S.; Sheng, G.; Boyd, S. A. Adv. Agron. 1997, 59, 25-62.    (6) Mishael, Y. G.; Undabeytia, T.; Rytwo, G.; Papahadjopoulos-Sternberg, B. Rubin, B.; Nir, S. J. Agric. Food Chem. 2002, 50, 2856-2863.    (7) Polubesova, T.; Nir, S.; Zadaka, D.; Rabinovitz, O.; Serban, C.; Groisman, L.; Rubin, B. Environ. Sci. Technol. 2005, 39, 2343-2348.    (8) Zadaka, D.; Polubesova, T.; Mishael, Y.; Spitzy, A.; Koehler, H.; Wakshal, E.; Rabinovitz, O.; Nir, S. Appl. Clay Sci. 2005, 29, 282-286.    (9) WO 2006/077583
These prior art documents are relevant for understanding the state of the art in the field of the invention. The references will be referred to in the text by giving their serial number from said list.
Pollution of groundwater and wells has become an environmental and economical hazard due to intensively irrigated agriculture and application of herbicides and pesticides over cultivated lands as well as waste spills within the catchment areas of the various hydrogeological basins (1).
Perchlorate anion (ClO4−), which is quite inert, is produced when salts of ammonium, or sodium perchlorate dissolve in water. One source of perchlorate in water arises from waste water of plants of solid rocket engine fuels. Another source is due to the use of certain fertilizers. At relatively large concentrations, perchlorate interferes with the body's iodine intake, causing disruption of thyroid gland functions (2, 3), although a safe daily exposure has not yet been agreed upon. Upper limits on perchlorate concentrations in drinking water in several states in USA vary between a few ppb and about twenty ppb. In Israel no official limit has been set, but many wells have been closed when perchlorate concentrations exceeded 24 ppb. Regions in the aquifer with perchlorate concentrations at 1000-fold higher than the above limit have been identified.
Chromium is a major pollutant arising from erosion of natural deposits, discharge from steel and metal refining industries, pulp mills, and a variety of manufacturing industries. Chromium is a known carcinogen, and hexavalent chromium as in chromate is mutagenic. In its hexavalent form chromium can be taken up by cells. Its allowed concentration in the hexavalent form is about 10 ppb.
Cyanides are compounds which contain the CN group. The major sources of cyanide released to water are metal finishing industries, iron and steel making industries and water treatment facilities. The most important metal-cyanide complexes are those of iron, zinc, nickel, copper cobalt and cadmium. Iron cyanocomplexes most commonly occur in various effluents (electropolating, gold mining, coal gasification), which photodissociate to free cyanide upon exposure to sunlight, which enhances significantly their toxicity. The upper limits on cyanide concentrations in drinking water vary between 50 and 200 ppb.
The adsorption of organic cations on clays partially transforms the clay-mineral surface from hydrophilic to hydrophobic (4, 5). The micelle-clay system is a relatively new innovation in which the structure includes a positively charged surface to a varying degree and a hydrophobic core (6,7).